It is known that aqueous suspensions of swollen vermiculite ore particles can be prepared by substituting monovalent inorganic cations such as Li.sup.+ or Na.sup.+ for exchangeable cations retained by the ore, particularly Mg.sup.2+ cations, followed by a subsequent step of aqueous washing to remove excess salt and effect macroscopic ore particle swelling. It is also known to employ a third step of introducing mechanical shearing action to the swollen ore particles in water to delaminate the vermiculite structure and to produce an aqueous dispersion of tiny particles or platelets of vermiculite known as vermiculite lamellae. Vermiculite lamellae or platelets can be further characterized as having a particle size typically less than 200 microns, preferably less than 50 microns, and having one dimension that is small compared to the other two dimensions with an aspect ratio (i.e., length or breadth divided by thickness) of at least 10, preferably at least 100 and more preferably at least 1,000, for example, 10,000.
For Li.sup.+ exchanged vermiculite ores, sufficient ore swelling occurs in the subsequent washing step such that application of a shearing action to the swollen ore particles reduces platelet dimensions to less than approximately 50 microns, thereby producing vermiculite lamellae of a preferable size for the fabrication of films and coatings. A process as such is disclosed in U.S. Pat. No. 3,325,340.
Salts of lithium have been preferred, as set forth above, due to the cation's capability of causing vermiculite ore to swell during the subsequent washing step prior to a shearing step such that vermiculite lamellae of the desired dimensions are produced. However, lithium salts are expensive, relative to other available inorganic salts.
Sodium salts, therefore, are the most common salt used in the treatment of vermiculite particles due to its low cost, availability and lack of environmental concerns. Na.sup.+ exchanged ores, however, lack the swelling potential of Li.sup.+ exchanged ores, and thus, are typically replaced by an organo-cation in a second exchange step, followed by a second aqueous washing step to swell the vermiculite ore to an adequate degree, preferably at least twice its original volume, and then subjected to a shearing action to delaminate the swollen ore particles and to produce vermiculite lamellae of a preferred size of less than 50 microns.
Such a process, as set forth above, is disclosed in U.S. Pat. No. 4,608,303 and U.K. Pat. No. 1,593,382. In this process, Na.sup.+ exchanged vermiculite ores are contacted with an aqueous organo-cation solution wherein organo-cation salts are intercalated into the vermiculite structure and exchanged for the Na.sup.+ cations. For example, in U.K. Pat. No. 1,593,382, Na.sup.+ exchanged vermiculite ore is contacted with aqueous solution of butylammonium chloride in a second exchange step to effect ore swelling in a subsequent aqueous washing step followed by application of a shearing action to delaminate the swollen ore particles.
It is preferred, in such processes, to perform the second exchange step wherein the concentration of the organo-cation in aqueous solution is higher than that of exchangeable ions in the Na.sup.+ exchanged vermiculite ore. Typically, molar ratios of 1:1 to 12:1 organo-cation to Na.sup.+ exchangeable ions in the ore can be employed.
In processes such as disclosed in U.S. Pat. No. 4,608,303 and U.K. No. 1,593,382, a swelling step subsequent to the step of contacting the Na.sup.+ exchanged vermiculite ore with organo-cations wherein the organo-cation intercalated ore is subjected to aqueous washing prior to subjecting the ore particles to a shearing action is crucial for the production of vermiculite lamellae of the desired size. It has been preferred to allow the swelling of the ore to proceed to at least four times its original volume, and in some aspects, six times the ore's original volume before shearing.
The swelling step, however, necessarily complicates the process of producing vermiculite lamellae with desired dimensions, and provides for the added production costs of equipment, and labor. Production time is also increased. Therefore, it is an object of this invention to provide an improved process for producing suspensions of vermiculite lamellae having dimensions of less than 200 microns, preferably less than 50 microns, by the elimination of separate washing and ore swelling steps.